1. Field of the Invention
The present invention relates to a multifunction probe intended for measuring the static and total pressures, as well as the angle of attack of the flow of a fluid near an aircraft. The probe is especially intended for measuring the flow parameters of the air near an airplane.
2. Discussion of the Background
The static pressure is a very important parameter for the safety of an airplane. An international standard establishes a correspondence between the static pressure and the altitude. This correspondence is used to associate an aircraft with an altitude in a unique manner by allocating it a static pressure value to be complied with during the flight thereof.
The total pressure is not utilized as it stands, but it makes it possible to determine the dynamic pressure by calculating the differential pressure between the total pressure and the static pressure. The dynamic pressure is a very important parameter since it makes it possible to determine the velocity of the air flow; the velocity of the air flow coming into play, for its part, in calculating the lift of the airplane.
The pressure measurements are performed by way of pressure taps. The first known probes were equipped with a single pressure tap. This limitation compelled the use of several probes in order to be able to perform the various pressure measurements.
The configuration customarily adopted comprises:
a static pressure probe for measuring the local static pressure Ps
a total pressure probe for measuring the total pressure Pt
and a vane for measuring the local angle of attack xcex1.
With such a configuration, the calculation of the parameters, static pressure Ps, total pressure Pt and local angle of attack xcex1, requires the accurate knowledge on the one hand of the characteristics of the three probes, and on the other hand of the aerodynamic field of the airplane at the points of position of the probes on the fuselage. Furthermore, each probe requires its de-icing system.
To remedy these drawbacks, the person skilled in the art may resort to a multifunction probe. A multifunction probe advantageously makes it possible to measure the above parameters at one and the same point of the airplane. Optimization of the position of the probe eases the calculations. The use of a multifunction probe makes it possible to reduce the number of probes, and consequently, it makes it possible to reduce the heating power required for de-icing. There are various types of multifunction probe.
A first type encompasses moveable multifunction probes. A probe of this type comprises a moveable part, generally referred to as the vane, which positions itself in the direction of the air stream and which carries static and total pressure taps. The manufacture of probes of this type presents significant difficulties. The vane compels a complex mechanical link with the fixed part of the probe. The link must allow rotation of the vane while ensuring continuity of the pressure ducts between the vane and the fixed part, while this continuity must not exhibit any leaks. Sealing is therefore difficult to achieve since it must be compatible with the rotation of the vane.
A second type encompasses fixed multifunction probes. A typical probe is described in the patent U.S. Pat. No. 4,096,744. This probe comprises pressure taps distributed at various locations of the probe. This distribution gives the possibility, after calculation, of accessing the altitude, velocity and angle of attack information. However, this probe comprises a total pressure tap Pt at the front extremity of the probe; this tap is often referred to by the name xe2x80x9cPitotxe2x80x9d. The Pitot tap renders the nose of the probe fragile. U.S. Pat. No. 5,628,565 describes an elaborate probe which is capable, simultaneously, of measuring various pressures and of measuring the temperature of the air stream. However, this probe is also equipped with a Pitot tap which renders the nose of the probe fragile.
An aim of the invention is to provide a fixed multifunction probe for aircraft which does not have the drawback recalled above.
Accordingly, the subject of the invention is a fixed multifunction probe for aircraft having a closed front part and having at least three pressure taps distributed in various sections at specified points of the body of the probe. The fixed multifunction probe according to the invention makes it possible to measure the flow parameters of the fluid moving with respect to the probe. To this end, it comprises:
a body having symmetry of revolution about a longitudinal axis, closed by a rounded cap, the body being placed in the flow,
at least three pressure taps situated at specified points of the body and distributed in various sections so as to tap a first pressure, a second pressure and a third pressure,
pressure measurement means associated with the pressure taps for measuring at least as many pressures P1, . . . , Pn as pressure taps,
calculation means for calculating the local angle of attack xcex1 of the flow by expressing a specified ratio of measured pressures as a function of the local angle of attack a in the form:             P1      -      P2              P1      +      P2        =            A      +                        B          ·          cos                ⁢                  xe2x80x83                ⁢        2        ⁢                  xe2x80x83                ⁢        α            +                        C          ·          sin                ⁢                  xe2x80x83                ⁢        2        ⁢                  xe2x80x83                ⁢        α                    D      +                        E          ·          cos                ⁢                  xe2x80x83                ⁢        2        ⁢                  xe2x80x83                ⁢        α            +                        F          ·          sin                ⁢                  xe2x80x83                ⁢        2        ⁢        α            
A, B, C, D, E, F being constants dependent solely on the coordinates of the pressure taps, the specified position of the pressure taps being such that the expression for the ratio as a function of the local angle of attack xcex1 is quasi linear,
and for calculating the total pressure Pt of the flow at the level of the probe, the static pressure at upstream infinity of the probe Ps∞ and the dynamic pressure Ptxe2x88x92Ps∞ from the pressure coefficients kP of the pressure taps.
By virtue of the absence of any Pitot pressure tap, a probe according to the invention is more robust than a fixed multifunction probe equipped with such a tap. Furthermore, the absence of a Pitot tap makes it possible to free up some room for installing a heating circuit, thereby making it possible to improve the de-icing of the extremity of the probe.
The fixed structure of the probe eases the inspection of the integrity of the probe before flight as well as the transmission of the heating energy and the pneumatic pressures. The structure of the probe allows installation at the nose of the airplane, in a similar manner to the installation of a nose boom, and also installation along the fuselage, by way of a mast acting as support and by way of a fixing pad.
According to a first embodiment of the invention, the probe comprises three pressure taps. The pressure taps are associated with pressure measurement means and with calculation means. The probe makes it possible to retrieve the local angle of attack, the total pressure and the static pressure of the aerodynamic flow in which it is placed. Advantageously the probe comprises no total pressure tap.
According to a second embodiment of the invention, the probe comprises a fourth pressure tap associated with pressure measurement means. Such a probe also makes it possible to retrieve the parameters listed above (local angle of attack, total pressure and static pressure of the flow), but with a securing of the information which the first embodiment does not allow. A fault with one of the pressure taps, or with one of the pressure measurement means, may be detected and signaled on completion of a comparison between the various values calculated from the various measurements. As in the first embodiment, the probe comprises no total pressure tap.